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Chiari Malformations

National Organization for Rare Disorders, Inc.

ImportantIt is possible that the main title of the report Chiari Malformations is not the name you expected.

Disorder Subdivisions

None

General Discussion

Summary

Chiari malformations are a group of complex brain abnormalities that affect the area in lower posterior skull where the brain and spinal cord connect. The underlying anatomy of Chiari malformations is thought to be present at birth (congenital), although in many cases they may not become clinically apparent until adulthood. In extremely rare cases, a Chiari malformation may be acquired during life. The exact cause of Chiari malformations are not known, but often the cavity near the base of the skull (posterior fossa) is narrow and abnormally small in relation to the size of the cerebellum, which this portion of the skull encloses. Researchers believe that in some cases the small posterior fossa may cause the developing brain, specifically the cerebellum and the brainstem, to be pushed downward. Part of the cerebellum (known as the cerebellar tonsils) may protrude (herniate) through the foramen magnum, which is the normal opening found in the occipital bone at the base of the skull. The tonsils may thus interfere with the flow of cerebrospinal fluid (CSF) to and from the skull and spinal canal, potentially leading to accumulation of cerebral spinal fluid in the subarachnoid spaces of the brain and spine. A Chiari malformation can also cause pressure on the brain and produce hydrocephalus (pressure due to excessive cerebrospinal fluid accumulation in the brain) and the spinal cord, potentially causing a wide variety of symptoms. In fact, no two cases of Chiari malformation are exactly alike and the associated symptoms are highly variable. The severity of Chiari malformations can vary dramatically as well. In some cases, affected individuals may not develop any symptoms (asymptomatic); in others, severe, potentially debilitating or life-threatening symptoms can develop.

Traditionally, Chiari malformations have been defined and classified by how much of the cerebellar tonsils protrude through the foramen magnum. A diagnosis of a Chiari malformation usually signifies that the cerebellar tonsils protrude below the foramen magnum (often cited as at least 5 millimeters, though this is controversial). However, researchers have determined that the length of tonsil descent in a Chiari malformation does not always correspond to the severity of symptoms or to the response to treatment. In fact, some individuals are classified as having Chiari malformation type 0, in which there is minimal or no descent of the cerebellar tonsils. These individuals still have symptoms associated with a Chiari malformation, most likely due to abnormalities in the flow of cerebrospinal fluid within the skull and spinal canal. Research is ongoing to understand the complex, underlying mechanisms that cause Chiari malformations.

Introduction

Chiari malformations are named for Hans Chiari, an Austrian pathologist, who first identified type I-III in 1891. Julius Arnold further expanded the definition of Chiari malformation type II and some medical sources began using the name Arnold-Chiari malformation. Nowadays, some medical sources use Arnold-Chiari malformation as a broad term for all forms. Chiari malformations have also been known as congenital tonsillar herniation, tonsillar ectopia or tonsillar descent.

Supporting Organizations

American Syringomyelia & Chiari Alliance Project, Inc.

P.O. Box 1586

Longview, TX 75606-1586

Tel: (903)236-7079

Fax: (903)757-7456

Tel: (800)272-7282

Email: info@asap.org

Website: http://www.asap.org

Birth Defect Research for Children, Inc.

976 Lake Baldwin Lane

Orlando, FL 32814

USA

Tel: (407)895-0802

Email: staff@birthdefects.org

Website: http://www.birthdefects.org

Chiari &#038; Syringomyelia Foundation

29 Crest Loop

Melville, NY 11747

Tel: (718)966-2593

Website: http://www.CSFinfo.org

Christopher S. Burton Syringomyelia Foundation, Inc.

P.O. Box 100335

Fort Lauderdale, FL 33310-0335

Tel: (954)727-5137

Fax: (954)636-2409

Email: info@thesmfoundation.org

Website: http://www.thesmfoundation.org

Conquer Chiari

320 Osprey Court

Wexford, PA 15090

USA

Tel: (724)940-0116

Fax: (724)940-0172

Email: director@conquerchiari.org

Website: http://www.conquerchiari.org

Hydrocephalus Association

4340 East West Highway Ste 950

Bethesda, MD 20814

USA

Tel: (301)202-3811

Fax: (301)202-3813

Tel: (888)598-3789

Email: info@hydroassoc.org

Website: http://www.hydroassoc.org

Hydrocephalus Support Group, Inc.

1933 Mistflower Glen Ct.

Chesterfield, MO 63005-4236

USA

Tel: (636)532-8228

Fax: (314)251-5871

Email: hydrob@earthlink.net

March of Dimes

1275 Mamaroneck Avenue

White Plains, NY 10605

Tel: (914)997-4488

Fax: (914)997-4763

Email: AskUs@marchofdimes.org or preguntas@nacersano.org

Website: http://www.marchofdimes.org and nacersano.org

NIH/National Institute of Neurological Disorders and Stroke

P.O. Box 5801

Bethesda, MD 20824

Tel: (301)496-5751

Fax: (301)402-2186

Tel: (800)352-9424

Website: http://www.ninds.nih.gov/

Spina Bifida Association of America

4590 MacArthur Boulevard NW

Suite 250

Washington, DC 20007-4226

Tel: (202)944-3285

Fax: (202)944-3295

Tel: (800)621-3141

Email: sbaa@sbaa.org

Website: http://www.sbaa.org

World Arnold Chiari Malformation Association

31 Newtown Woods Road

Newtown Square, PA 19073

Tel: (610)353-4737

Email: chiari-owner@yahoogroups.com

Website: http://www.wacma.com

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). For a full-text version of this report, go to www.rarediseases.org and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only.

It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report.

This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

Last Updated: 3/5/2014Copyright 2014 National Organization for Rare Disorders, Inc.

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